Arthritis of the knees can wear away and destroy the surfaces of the knee joint and ultimately lead to conditions that require a knee replacement. In osteoarthritis, which is usually caused by old age, angular deformity, or old fractures, the surfaces of the knee gradually wear out. Likewise systemic arthritis affects the synovium or membrane tissue in the joint destroying the surface of the joint. In both osteoarthritis and systemic arthritis, when the surface of the joint is worn away, walking and other activities become difficult and painful. In many cases, knee replacements are performed to address these issues.
Knee replacement surgery or arthroplasty typically involves a resurfacing of the knee joint in which the femur, or thigh bone, and/or tibia, or shinbone, are covered with artificial materials such as metal or plastic thereby replacing the irregular surfaces caused by the arthritis with smooth surfaces. The undersurface of the patella, or knee cap, may also be replaced with artificial materials. Historically, the actual knee replacement procedure involved either general or epidural anesthesia with a four to six day hospitalization with the surgery itself taking about two hours.
There are three general types of knee replacements: total knee replacements (TKR), partial knee replacement (also called a unicompartmental knee replacement), and knee revision. A TKR resurfaces the knee joint by removing the diseased bone and cartilage. The end of the long bones of the knee joint, the femur and the tibia, are removed and replaced with artificial materials. The portion of the femur that is removed is usually replaced with metal (e.g. titanium or zirconium), while the portion of the tibia that is removed is usually replaced with plastic. The replacement components may be either cemented in place or inserted in a cementless manner.
A partial knee replacement involves installing an implant on one side of the knee, rather than over the entire surface of the knee joint. A unicondylar knee replacement is done if part of the knee joint is damaged by arthritis and the other compartments have healthy, normal cartilage at surgery.
A knee revision involves fixing problems with an existing knee replacement. Knee replacements fail over time and require revision. This revision procedure may be more complex than a total knee replacement for a number of reasons including because removing the existing implant may weaken the bone and damage the surrounding ligaments supporting the knee. Because of these problems a special implant may be used or a bone graft may be required to reconstruct deficient areas.
Traditional instrumentation and surgical techniques used in open arthroplasty surgery are not easily adapted for use in minimally invasive knee surgery. Specifically, using traditional instrumentation with smaller incisions can lead to stretching of the skin and misalignment of the knee replacement components due to lack of visibility. Using nontraditional surgical techniques, on the other hand, provides the disadvantage of requiring the surgeon to re-learn the surgery and can lead to longer operative times, higher complication rates, and higher surgical costs.